Techniques have been performed that measure an electrical characteristic of a sample, and determine a physical property of the sample from the measurement result, and/or determine the type of cells and/or the like contained in the sample (see, e.g., Patent Document 1). Examples of electrical characteristic measured include a complex permittivity and its frequency dispersion (dielectric spectrum). A complex permittivity and its frequency dispersion are typically calculated by applying an electrical voltage (hereinafter referred to simply as “voltage”) to the sample solution, and then measuring a complex capacitance or a complex impedance across electrodes.
In addition, for example, Patent Document 2 discloses a technology for obtaining information relating to blood coagulation from an electrical permittivity (hereinafter referred to simply as “permittivity”) of the blood, and describes “a blood coagulation system analysis device including: a pair of electrodes; application means for applying an alternating voltage to the pair of electrodes at predetermined time intervals; measurement means for measuring a permittivity of blood which is positioned between the pair of electrodes; and analysis means for analyzing a degree of the action of a blood coagulation system by using the permittivity of blood which is measured at the time intervals after the anticoagulant effect acting on the blood is ended.”
Electrical measurement of a biological sample such as one described above typically uses a method that obtains a state of the biological sample by applying a signal in multiple frequency bands to the biological sample, and receiving a response therefor. Response acquisition methods using multiple frequencies include a method that divides time for acquiring a response for a single frequency band (time-division method), and a method that acquires a response by synthesizing an application signal at one time (frequency-multiplexing method).
An example of time-division method is illustrated in FIG. 8. In this example, a response is acquired in three frequencies, which are 100 kHz, 1 MHz, and 10 MHz, in each measurement, and eight measurements are performed at each frequency. Thus, the measurement in each frequency is performed such that multiple measurements are performed at time intervals, and the measured values are then averaged to cancel out variation between measurements. The signal-to-noise ratio (SNR) is thus improved.
An example of frequency-multiplexing method is illustrated in FIG. 9. In this example, a method is used in which signals having a same amplitude and respectively having frequencies of 100 kHz, 1 MHz, and 10 MHz (three signals in the lower part of the diagram) are superimposed; the superimposed signal (the topmost signal in the diagram) is obtained; and this signal is then applied to the analyte to obtain a response. During the measurements, similarly to the time-division multiplexing described above, multiple measurements are performed, and the measured values are then averaged to cancel out variation between measurements. The SNR is thus improved. This example illustrates an example of performing 24 measurements during the entire time span (in FIG. 9, one second).